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Search Results: 1 - 10 of 20847 matches for " Jean Geringer "
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Fracture simulation for zirconia toughened alumina microstructure
Kyungmok Kim,Jean Geringer,Bernard Forest
Physics , 2013, DOI: 10.1108/EC-08-2013-0163
Abstract: Purpose - The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures. Design/methodology/approach - A two-dimensional finite element model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$ microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models. Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about the increase of crack density rate. Social implications - This paper is the first step for predicting the lifetime of ceramic implants. The social implications would appear in the next few years about health issues. Originality/value - This proposed finite element method allows describing fracture and fatigue behaviours of alumina-zirconia microstructures for hip prosthesis, provided that a microstructure image is available.
Influence of proteins from physiological solutions on the electrochemical behaviour of the Ti-6Al-4V alloy: reproducibility and time-frequency dependence. ---- Influence de la teneur en protéines de solutions physiologiques sur le comportement électrochimique du Ti-6Al-4V : reproductibilité et représentation temps-fréquence
Jean Geringer,Laurent Navarro,Bernard Forest
Quantitative Biology , 2010, DOI: 10.1051/mattech/2010020
Abstract: The electrochemical behaviour of the biomedical and metallic alloys, especially in the orthopaedic implants fields, raises many questions. This study is dedicated for studying the Ti-6Al-4V alloy, by electrochemical impedance spectroscopy, EIS, in various physiological media,: Ringer solution, phosphate buffered solution (PBS), PBS solution and albumin, PBS solution with calf serum and PBS solution with calf serum and an antioxidant (sodium azide). Moreover, the desionised water was considered as the reference solution. The tests reproducibility was investigated. The time-frequency-Module graphs highlighted that the desionised water is the most protective for the Ti-6Al-4V alloy. This biomedical alloy is the less protected in the solution constituted by PBS and albumin. The time-frequency graph allows pointing out the graphic signatures of adsorption for organic and inorganic species (differences between the modules means in studied solution and the modules mean in the reference solution). --- Le comportement \'electrochimique des alliages m\'etalliques biom\'edicaux, notamment dans le domaine des implants orthop\'ediques, pose encore de nombreuses questions. Ce travail propose d'\'etudier l'alliage de titane Ti-6Al-4V, par spectroscopie d'imp\'edance \'electrochimique, SIE, dans diff\'erents milieux physiologiques : solution de Ringer, solution \`a base d'un tampon phosphate (PBS), solution PBS avec de l'albumine, solution PBS avec du s\'erum bovin et une solution PBS avec du s\'erum bovin et un antioxydant (azoture de sodium). De plus, une solution d'eau ultra-pure servira de r\'ef\'erence. La reproductibilit\'e des tests a \'et\'e \'etudi\'ee. Les repr\'esentations temps-fr\'equence des modules ont mis en \'evidence que l'eau d\'esionis\'ee est la solution qui pr\'esente le caract\`ere le plus protecteur pour le Ti-6Al-4V. Cet alliage de titane est le moins prot\'eg\'e dans la solution de PBS contenant de l'albumine. Cette repr\'esentation permet de mettre en \'evidence des signatures graphiques d'adsorption des esp\`eces inorganiques et organiques (diff\'erences entre les moyennes des modules dans les solutions \'etudi\'ees et la moyenne des modules dans la solution de r\'ef\'erence).
Predicting the steady state thickness of passive films in order to prevent degradations of implant
Jean Geringer,Mathew L. Taylor,Digby D. Macdonald
Physics , 2014,
Abstract: Some implants have approximately a lifetime of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel. Fretting corrosion, friction under small displacements, should occur during human gait, due to repeated loadings and un-loadings, between stainless steel and bone for instance. Some experimental investigations of fretting corrosion have been practiced. As well known, metallic alloys and especially stainless steels are covered with a passive film that prevents from the corrosion and degradation. This passive layer of few nanometers, at ambient temperature, is the key of our civilization according to some authors. This work is dedicated to predict the passive layer thicknesses of stainless steel under fretting corrosion with a specific emphasis on the role of proteins. The model is based on the Point Defect Model (micro scale) and an update of the model on the friction process (micro-macro scale). Genetic algorithm was used for finding solution of the problem. The major results are, as expected from experimental results, albumin prevents from degradation at the lowest concentration of chlorides; an incubation time is necessary for degrading the passive film; under fretting corrosion and high concentration of chlorides the passive behavior is annihilated.
Degradation of alumina and zirconia toughened alumina (ZTA) hip prostheses tested under microseparation conditions in a shock device
Juliana Uribe,Jean Geringer,Laurent Gremillard,Bruno Reynard
Physics , 2013, DOI: 10.1016/j.triboint.2012.10.002
Abstract: This paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was found to have a higher wear resistance compared to alumina.
Predicting the steady state thickness of passive films with the Point Defect Model in fretting corrosion experiments
Jean Geringer,Digby D. Macdonald,Mathew L. Taylor
Physics , 2013, DOI: 10.1051/matecconf/20130704001
Abstract: Some implants have approximately a lifetime of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel. Fretting corrosion, friction under small displacements, should occur during human gait, due to repeated loadings and un-loadings, between stainless steel and bone for instance. Some experimental investigations of fretting corrosion have been practiced. As well known, metallic alloys and especially stainless steels are covered with a passive film that prevents from the corrosion and degradation. This passive layer of few nanometers, at ambient temperature, is the key of our civilization according to some authors. This work is dedicated to predict the passive layer thicknesses of stainless steel under fretting corrosion with a specific emphasis on the role of proteins. The model is based on the Point Defect Model (micro scale) and an update of the model on the friction process (micro-macro scale). Genetic algorithm was used for finding solution of the problem. The major results are, as expected from experimental results, albumin prevents from degradation at the lowest concentration of chlorides; an incubation time is necessary for degrading the passive film; under fretting corrosion and high concentration of chlorides the passive behavior is annihilated. Les implants orthop\'ediques de hanche ont une dur\'ee de vie d'environ 15 ans. Par exemple, la tige f\'emorale d'un tel implant peut \^etre r\'ealis\'ee en acier inoxydable 316L ou 316LN. Le fretting corrosion, frottement sous petits d\'eplacements, peut se produire pendant la marche humaine en raison des chargements r\'ep\'et\'es entre le m\'etal de la proth\`ese et l'os. Plusieurs investigations exp\'erimentales du fretting corrosion ont \'et\'e entreprises. Cette couche passive de quelques nanom\`etres, \`a temp\'erature ambiante, est le point clef sur lequel repose le d\'eveloppement de notre civilisation, selon certains auteurs. Ce travail vise \`a pr\'edire les \'epaisseurs de cette couche passive de l'acier inoxydable soumis au fretting corrosion, avec une attention sp\'ecifique sur le r\^ole des prot\'eines. Le mod\`ele utilis\'e est bas\'e sur le Point Defect Model, PDM (\`a une \'echelle microscopique) et une am\'elioration de ce mod\`ele en prenant en compte le processus de frottement sous petits d\'ebattements. L'algorithme g\'en\'etique a \'et\'e utilis\'e pour optimiser la convergence du probl\`eme. Les r\'esultats les plus importants sont, comme d\'emontr\'e avec les essais exp\'erimentaux, que l'albumine, la prot\'eine \'etudi\'ee, emp\^eche les
Acroteriasis congenita dans la race pie noire des plaines en pologne
H Geringer
Genetics Selection Evolution , 1969, DOI: 10.1186/1297-9686-1-1-15
Abstract:
Finite Element Modelling of Shock-Induced Damages on Ceramic Hip Prostheses
Juliana Uribe,Jérôme Hausselle,Jean Geringer,Bernard Forest
ISRN Materials Science , 2011, DOI: 10.5402/2011/121486
Abstract:
Les annales de génétique et de sélection animale: un bilan des cinq premières années
JJ Lauvergne, HK Geringer
Genetics Selection Evolution , 1974, DOI: 10.1186/1297-9686-6-1-159
Abstract:
Extracting the unresolved pulsar contribution to the gamma-ray background
Alex Geringer-Sameth,Savvas M. Koushiappas
Physics , 2011, DOI: 10.1111/j.1365-2966.2012.20453.x
Abstract: We present a statistical framework which can be used to determine the contribution of an unresolved population of pulsars to the gamma-ray background. This formalism is based on the joint analysis of photon time series over extended regions of the sky. We demonstrate the robustness of this technique in controlled simulations of pulsar populations, and show that the Fermi Gamma-ray Space Telescope can be used to detect a pulsar contribution as small as 0.1% of the gamma-ray background. This technique is sensitive to pulsar populations with photon fluxes greater than ~1E-10 cm^-2 s^-1. The framework is extensible to arbitrarily complex searches for periodicity and can therefore be tailored to specific applications such as all-sky surveys and studies of the Galactic center and globular clusters.
Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs with Fermi
Alex Geringer-Sameth,Savvas M. Koushiappas
Physics , 2011, DOI: 10.1103/PhysRevLett.107.241303
Abstract: Dwarf spheroidal galaxies are known to be excellent targets for the detection of annihilating dark matter. We present new limits on the annihilation cross section of Weakly Interacting Massive Particles (WIMPs) based on the joint analysis of seven Milky Way dwarfs using a frequentist Neyman construction and Pass 7 data from the Fermi Gamma-ray Space Telescope. We exclude generic WIMP candidates annihilating into b-bbar with mass less than 40 GeV that reproduce the observed relic abundance. To within 95% systematic errors on the dark matter distribution within the dwarfs, the mass lower limit can be as low as 19 GeV or as high as 240 GeV. For annihilation into tau+tau- these limits become 19 GeV, 13 GeV, and 80 GeV respectively.
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